1. Field of Invention
The present invention relates to a wafer electroplating apparatus. More particularly, the present invention relates to a wafer electroplating apparatus with functions of bubble removal and flow rectification.
2. Description of Related Art
Electroplating is to employ an object to be plated as a cathode, such as a semiconductor wafer, and a plating metal as an anode, such as titanium plated with platinum or titanium, and apply a voltage between the cathode and anode to allow metal to ionize. Metal ions are then deposed on the object to be plated, which increases the surface brightness and the corrosion resistance of the object to be plated. Following the rapid development of the integrated circuit (IC), the quality requirements for wafer electroplating is becoming more and more demanding for fulfilling the increasing needs of IC applications.
Bubbles may be generated during an electroplating process and circulate along with the electroplating solution in pipelines. Defects may be caused in the object to be plated due to the existence of these bubbles in the electroplating solution and becomes a main issue in an electroplating process. JP 2003-277986 disclosed a debubbler with functions of removing bubbles and flow rectification. However, the debubbler is a complicated structure and requires high cost and huge space, and an inbuilt area for bubble removal is also not convenient to be cleaned. There is another conventional electroplating apparatus equipped with a de-bubble tank below an electroplating bath, but many circulating dead spaces are present in the rectangular de-bubble tank which leads to exceptional deposition, unsymmetrical flow field and difficulty in cleaning.
Electroplating involves an electrochemical process in which exchange of ion charges occurs, that is, charge transfer. Therefore, flow field distribution of the electroplating solution has an impact on electroplating. Flow field distribution of the electroplating solution entering an electroplating bath is rendered unsymmetrical if the length of a pipe is insufficient or an angular deviation of the pipe exists. Unsymmetrical flow field distribution results in making the distributions of concentration and flow speed of the electroplating solution in the electroplating bath irregular and also influences uniformity in electroplating thickness. U.S. patent application Ser. No. US10/743,496 disclosed an electroplating apparatus to which a rectification device is added for rectifying the electroplating solution prior to entering an electroplating tank. The added height of the electroplating tank due to the built-in rectification device increases the required amount and cost of electroplating solution, and the presence of bubbles in the electroplating solution in pipes remains a factor in electroplating yield.